This invention relates to transformers and more particularly to a coil bus for a transformer.
As is well known, a transformer converts electricity at one voltage to electricity at another voltage, either of higher or lower value. A transformer achieves this voltage conversion using a primary coil and a secondary coil, each of which are wound on a ferromagnetic core and comprise a number of turns of an electrical conductor. The primary coil is connected to a source of voltage and the secondary coil is connected to a load. The ratio of turns in the primary coil to the turns in the secondary coil (“turns ratio”) is the same as the ratio of the voltage of the source to the voltage of the load. Two main winding techniques are used to form coils, namely layer winding and disc winding. The type of winding technique that is utilized to form a coil is primarily determined by the number of turns in the coil and the current in the coil. For high voltage windings with a large number of required turns, the disc winding technique is typically used, whereas for low voltage windings with a smaller number of required turns, the layer winding technique is typically used.
In the layer winding technique, the conductor turns required for a coil are typically wound in one or more concentric conductor layers connected in series, with the turns of each conductor layer being wound side by side along the axial length of the coil until the conductor layer is full. A layer of insulation material is disposed between each pair of conductor layers.
A different type of layer winding technique is disclosed in U.S. Pat. No. 6,221,297 to Lanoue et al., which is assigned to the assignee of the present application, ABB Inc., and which is hereby incorporated by reference. In the Lanoue et al. '297 patent, alternating sheet conductor layers and sheet insulating layers are continuously wound around a base of a winding mandrel to form a coil. The winding technique of the Lanoue et al. '297 patent can be performed using an automated dispensing machine, which facilitates the production of a layer-wound coil.
In the layer winding technique utilizing sheet conductor layers, the ends of the sheet conductor of the coil are secured to coil bus bars that extend vertically (along the axis of the coil) to a top or a bottom of the coil, depending on the construction of the transformer in which the coil is mounted. The coil bus bars are usually secured to the sheet conductor by welding. Conventionally, the coil bus bars are formed of metal (such as copper or aluminum) and are rectangular in shape. Typically, the two coil bus bars are formed from a single rectangular bar by cutting the bar in half with a cut made perpendicular to the length of the bar.
In order to reduce the cost of a transformer, it is desirable to reduce the amount of metal (particularly copper) that is used in the transformer. The present invention is directed to coil bus bars that utilize less metal than conventional coil bus bars.